'A2 BOTANY 



has existed for a long period, the adaptation of the plants to their 

 peculiar environment and the competition with other plants results 

 in a much specialized flora, and such isolated regions always show 

 a very high proportion of " endemic " or peculiar species. It has 

 been estimated that about eighty per cent of the Dicotyledons of 

 Hawaii are endemic, and in Australia the proportion is probably 

 almost as great. In the case of such volcanic islands as Hawaii, the 

 ancestors of the existing flora must have reached the islands at vari- 

 ous times, and from different sources ; but in Australia the ancestors 

 of most of the existing plants already existed in the Tertiary flora of 

 the continent. 



Alpine Floras. Another type of isolated flora is seen in the 

 Alpine vegetation of high mountains. 



There is a remarkable similarity in the character of the plants 

 of high mountains in widely separated parts of the world, and in all 

 cases the Alpine plants belong to northern types, which often are not 

 found elsewhere within long distances. Thus upon the summits of 

 mountains within the Tropics, one may encounter plants of famil- 

 iar northern genera, which are quite wanting in the adjacent low- 

 lands. The writer has collected upon the summit of the Blue 

 Mountains of Jamaica, some 7000 feet above sea-level, such north- 

 ern plants as Strawberries, Brambles, Buttercups, and others much 

 like the species of the northern United States, but quite unknown 

 elsewhere upon the island or the adjacent mainland. 



Upon the summits of the White Mountains, the little Greenland 

 Sandwort (Arenaria Groenlandica) is familiar to every one who has 

 climbed these mountains, and other far northern plants occur upon 

 the summits of the New England mountains. 



The explanation usually offered for the presence of these plants, so 

 far away from their original home, is that, driven southward by the 

 advancing ice, some of them, instead of following the retreating ice 

 northward, were stranded on the mountains up which they were com- 

 pelled to ascend, as the increasing temperature of lowlands became 

 unfitted to their needs, and the competition with the plants better 

 fitted to the warmer climate compelled them to retreat. 



Similarities in Remote Regions. There are sometimes found two 

 regions, geographically far apart, which show much greater simi- 

 larity than do those much nearer to 'each other. Probably the best- 

 known case is that of the remarkable correspondence between the 

 flora of temperate Eastern Asia, and the corresponding region of 

 North America. The similarity of the vegetation in these two 

 regions is far greater than that between California and either of the 

 regions in question, and what is perhaps more extraordinary, than 

 that which exists between Eastern Asia and Europe, although there 

 is continuous land communication between these two continents. 



